Preparation of esters

ABSTRACT

The esterification of carboxylic acids with carbinols is effected in the presence of a catalyst comprising a palladium salt or palladium complex at esterification conditions. The reaction is exemplified by the reaction of benzoic acid with benzyl alcohol in the presence of palladium acetate to produce benzyl benzoate.

United States Patent [1 1 Massie 1 Jan. 30, 1973 [54] PREPARATION OFESTERS [56] References Cited [75] Inventor: Stephen N. Massie Palatine,Ill. 7 UNITED STATES PATENTS [73] Assignee: Universal Oil ProductsCompany, 1,908,708 5/1933 Krchma et al...-... ..260/488 Des Plaines lll.3,534,088 l0/l970 Bryant 'et al. ..260/476 [22] Filed: 1970 I PrimaryExaminerLorraine A. Wcinberger [21] A No; 70,620 Assistant Examiner-R S.Weissberg Attorney-James R. Hoatson, Jr. and Raymond H. N l 521 U.S. c|..260/476 R, 260/32614, 260/32 6.3, e v

260/410.5, 260/410.9 R, 260/468 R, 260/471 [57] ABSTRACT A, 260/479 R,260/479 S, 260/482 R,

260/486 R, 2 0 43g CD, 2 01433 F The esterification of carboxylic acidswith carbmols IS 51 Im. on. ....C07c 69/14, C076 69/54, C07C 69/78effected in the Pr of a catalyst p s P 53 i l f Search 3 0 47 R, 43 R, 43 ladium salt or palladium complex at esterification conditions. Thereaction is exemplified by the reaction of berlzoic acid with benzylalcohol in the presence of palladium acetate to produce benzyl benzoate.

9 Claims, N0 Drawings PREPARATION OF ESTERS This invention relates to aprocess for producing esters, and more particularly to a process forreacting a carboxylic acid with a carbinol in the presence of certaincatalytic compositions of matter of the type hereinafter set forth ingreater detail. The use of esters in the chemical field is well known.For example, benzyl acetate is used as an essential ingredient ofartificial jasmin and other flowery perfumes, in soap perfumes, in someflavors, in natural and synthetic resins, oils, lacquers, etc.; benzylbenzoate is used as a fixative and solvent for musk in perfumes andflavors, in medicines, as a plasticizer; benzyl propionate is also usedin perfumes; methyl methacrylate is used in polymers and co-polymers;ethyl acrylate is used in polymers, acrylic paints and as a chemicalintermediate; ethyl acetate is used as a lacquer and plastic solvent, inflavoring, perfurnery, artificial fruit essences, as a smokeless powderetc. In addition, the esters resulting from the use of an amino acidsuch as alanine, glycine, etc., are used in medicines, in biochemicalresearch, resins, etc.

It is therefore an object of this invention to provide a process forobtaining esters.

A further object of this invention is to provide a process for reactinga carboxylic acid and a carbinol utilizing certain catalyticcompositions of matter.

In one aspect an embodiment of this invention resides in a process forthe preparation of an ester which comprises reacting a carboxylic acidwith an alcohol in the presence of a palladium-containing catalyst atesterification conditions, and recovering the resultant ester.

A specific embodiment of this invention is found in a process for thepreparation of an ester which comprises reacting benzoic acid withbenzyl alcohol in the presence of a catalyst comprising palladiumacetylacetonate at a temperature in the range of from about 100 to about250 C. and a pressure in the range of from about atmospheric to about100 atmospheres and recovering the resultant benzyl benzoate.

Other objects and embodiments will be found in the following furtherdetailed description of the present invention.

As hereinbefore set forth the present invention in concerned with aprocess for preparing esters by reacting a carboxylic acid with acarbinol in the presence of certain catalytic compositions of matter asthe type hereinafter set forth in greater detail. By utilizing the,

catalytic compositions of matter of the present invention, it ispossible to effect the esterification reaction under neutral conditions,no acid being present. This will be of particular advantage whenesterifying certain compounds which possess a delicate structure whichis particularly sensitive to acids and which may be destroyed to someextent during the esterification reaction thus resulting in a loss ofthe ultimate yield of the desired product. In addition, it also willpermit a single step esterification process when esterifying thesecompounds inasmuch as those compounds which possess a delicate structuredo not have to be protected. When such compounds are subjected to anesterification reaction utilizing acidic conditions, it is necessary, inmany instances, to protect the structure in such a way so that anintermediate step is required, thus necessitating a more involved andintricate process with a corlysine,

responding increase in the cost of the final product. However, byutilizing the catalytic compositions of matter of the present process,it is possible, as hereinbefore set forth, to effect the esterificationreaction in a single step with a corresponding increase in yield of thedesired product.

The esterification conditions under which the reaction of the presentprocess is effected will include elevated temperatures in a range offrom about up to about 250 C. or more and at a pressure in the range offrom atmospheric up to about 100 atmospheres or more. The amount ofpressure which is utilized to effect the reaction will be dependent uponthe particular reactants which are undergoing esterification as well asthe temperature at which the reaction is effected, the amount ofpressure which is used being that which is necessary to maintain themajor portion of the reactants in the liquid phase. In the event thatsuperatmospheric pressures are employed, said pressures are provided forby the introduction of a substantially inert gas such as nitrogen intothe reaction vessel. In addition, the residence time which is requiredto effect the reaction will range from about 0.5 up to about 20 hours ormore in duration, said reaction time also being dependent upon theparticular reactants which are employed as well as the operatingconditions of temperature and pressure which are used.

Examples of carboxylic acids which are utilized as one of the startingmaterials in the esterification process of the present invention willinclude aliphatic acids, amino acids, cycloaliphatic acids, aromaticacids, etc. Some representative examples of these acids which may beemployed include aliphatic acids, both saturated and unsaturated innature, containing from two to about 20 carbon atoms in length such asacetic acid, propionic acid, butyric acid, valeric acid, caproic acid,enanthylic acid, caprylic acid, pelargonic acid,

capric acid, undecylic acid, lauric acid, tridecoic acid,

myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearicacid, nondecylic acid, arachidic acid, etc,; unsaturated aliphaticacids-such as acrylic acid, crotonic acid, isocrotonic acid, vinylacetic acid, methylacrylic acid, tiglic acid, angelic acid, senesioicacid, the isomeric hexenic acids, heptenic acids, octenic acids, etc.;amino substituted aliphatic acids such as glycine, alanine, alaine,norvaline, leucine, norleucine, isoleucine, isovaline, phenylalanine,tyrosine, serine, proline, tryptophane, hydroxyproline, arginine,omithine, asparagine, citrulline, etc.; cycloaliphatic acids such ascyclopentanecarboxylic acid, cyclohexanecarboxylic acid,cycloheptanecarboxylic acid, etc.; aromatic acids such as benzoic acid,o-toluic acid, m-toluic acid,p-toluic acid, alpha-phenylacetic acid,beta-phenylpropionic acid, gamma-phem ylbutyric acid, etc.

Examples of carbinols both saturated and unsaturated, which are utilizedas the other reactants in the process of this invention includealiphatic alcohols such as methyl alcohol, ethyl alcohol, propylalcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol,tert-butyl alcohol, the isomeric amyl, hexyl, heptyl, octyl, nonyl,decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl,heptadecyl, octadecyl, nonadecyl, eicosene alcohols, etc.;cycloaliphatic alcohols such as cyclopentanol, cyclohexanol,cycloheptanol, etc.; aromatic alcohols such as phenol benzyl alcohol,occresol, m-cresol, p-cresol, the xylenols,

temperature. Any excess pressure which may be mesitol, 2-phenylethanol,3-phenylpropanol, 4-phenylbutanol, 5-phenylpentanol, etc. It is to beunderstood that the aforementioned carboxylic acids and carbinols areonly representative of the class of compounds which may be used, andthat the present invention is not necessarily limited thereto.

The reaction'between the aforementioned carboxylic acids and carbinolsis effected in the presence of a catalytic composition of matter whichcomprises a palladium containing compound, the salts or complexes ofpalladium-being utilized therefor. Some representative examples ofpalladium containing compoundswhich .act as catalysts for the esterreaction include inorganic palladium salts such as palladium chloride,palladium bromide, palladium iodide, palladium nitrate, palladiumsulfate, palladium phosphate, etc.; organic palladium containingcompounds such as palladium acetate, palladium acetylacetonate,palladium propionate, palladium butyrate, etc.; or complexes such as anallylpalladium chloride dimer, dichlorobis(trimethylphosphine)(trimethylphosphine) palladium(ll), etc. It is contemplated within thescope 'of this invention that salts or complexes of other noble metalsof Group VIII of the Periodic Table may also be utilized'as catalystsfor the esterification reaction, although not necessarily that which issoluble in the solvent which is utilized,

said solvent including aromatic compounds such as benzene, toluene,o-xylene, m-xylene, p-xylene, ethylbenzene, etc. As hereinbefore setforth this is preferred inasmuch as the reaction may be effected in asingle phase.

The process suitable manner and may comprise a batch or continuous typeoperation. For example, when a batch type operation is useda quantity ofthe carboxylic acid and the carbine] is placed in an appropriateapparatus along with the palladium containing catalyst and, if sodesired, an organic solvent of the type hereinbefore set forth. Thereaction apparatus may comprise a flask provided with heating andstirring means or an autoclave of the rotating or the mixing type ifsuperatmospheric pressures are to be employed. In the event thatsuperatmospheric pressures. are used, the autoclave is sealed and aninert gas such as nitrogen is pressured in until the desired operatingpressure has been reached. Following this, the reaction apparatus isthen heated to the desired operating temperature and maintained thereatfor a predetermined residence time in the range also hereinbefore setforth. Upon completion of the desired reactiontime, heating isdiscontinued and the apparatus allowed to return to room of thisinvention may be effectedin any present is discharged, the apparatus isopened and the reaction mixture is recovered. The mixture is thensubjected to conventional means of separation including fractionaldistillation whereby the desired ester is separated and recovered fromany unreacted starting materials, side products, catalysts and solvent.

. It is contemplated within the scope of this invention that the processmay be effected in a continuous manner of operation. When such a type ofoperation is utilized, the starting materials comprising a carboxylicacid and a carbinol are continuously charged to the reaction zone whichis maintained at the proper operating conditions of temperature andpressure. In addition, thecatalyst and solvent are also continuouslycharged to the zone through a separate line, if so desired, thecatalyst-solvent solution may be admixed with one or both of thestarting materials prior to entry into said reactor and charged thereto.Upon completion of the desired reaction time, the reactor effluent iscontinuously withdrawn and subjected to separation steps whereby thedesired ester is separated and recovered, the unreacted startingmaterials, catalyst, and solvent being recycled to the reaction zone toform a portion of the feed stock.

Some representative examples of esters which may be prepared accordingto the process of this invention will include methyl acrylate, methylmethacrylate, methyl crotonate, ethyl acrylate, ethyl methacrylate,ethyl crotonate, propyl acrylate, propyl methacrylate, propyl crotonate,ethyl acetate, ethyl propionate, ethyl butyrate, ethyl valerate, propylacetate, propyl propionate, propyl butyrate, methyl benzoate, ethylbenzoate, propyl benzoate, benzyl acetate, benzyl propionate, benzylbutyrate, benzyl valerate, benzyl acrylate, benzyl methacrylate, benzylcrotonate, benzyl benzoate,etc.

The following examples are given to illustrate the process of thepresent invention which, however, are

not intended to limit the generally broad scope of the present inventionin strict accordance therewith.

EXAMPLE I In this example 3.1 g. of benzoic acid, 0.6 g. of benzylalcohol and 50 g. of toluene were placed in the glass liner of'arotating autoclave along with 1.0 g. of palladi um acetylacetonate. Theautoclave was sealed and nitrogen pressed in until an initial operatingpressure'of 35 atmospheres was reached. The autoclave was then heatingwas discontinued and the autoclave allowedto return toroom temperature.After the autoclave hadheated to a temperature of C. and maintainedthereat for a period of 16 hours. At the end of this time,

returned to room temperature, the excess pressure was discharged, theautoclave was opened and thereaction mixture was recovered. The mixturewhich comprises a red-amber-liquid was extracted with caustic to removethe excess benzoic acid. The caustic-soluble matter was dried by usinganhydrous potassium carbonate and sub jected to quantative gas-liquidchromatographic analysis which disclosed the presence of benzylbenzoate, no benzyl alcohol remaining unreacted.

EXAMPLE ii In this example 60.0 g. of acetic acid and 30.0 g. of benzylalcohol along with 1.0 g. of a catalyst comprising palladium acetate and40.0 g. of benzene are placed in the glass liner of a rotating autoclavewhich is thereafter sealed. Nitrogen is then pressed in until an initialpressure of 30 atmospheres is reached and thereafter the autoclave isheated to a temperature of 175 C. After maintaining this temperature fora period of 16 hours, heating is discontinued and the autoclave isallowed to return to room temperature. After returning to roomtemperature, the excess pressure is discharged, the autoclave is openedand the reaction mixture is recovered. After treatment in a mannersimilar to that set forth in Example 1 above, a gas-liquidchromatographic analysis will verify that the product is the desiredbenzyl acetate.

EXAMPLE III In like manner, 44.0 g. of butyric acid and 54.0 g. ofbenzyl alcohol are reacted in the presence of a catalyst comprisingpalladium chloride, said reaction conditions including a temperature of175 C., a pressure of 30 atmospheres of nitrogen and a reaction time of16 hours. After discontinuation of the heating, discharge of the excesspressure and recovery of the reaction mixture, the desired productcomprising benzyl butyrateis recovered.

EXAMPLE IV In this example 72.0 g. of acrylic acid and 88.0 g. ofanhydrous ethyl alcohol along with 1.0 g. of palladium acetyl-acetonateand 200.0 g. of benzene are placed in the glass liner of a rotatingautoclave. The liner is then sealed into the autoclave, flushed withnitrogen and nitrogen pressed in until an initial pressure of -30atmospheres is reached. The autoclave is then heated to a temperature of120 C. and maintained thereat for a period of 16 hours. At the end ofthis time period, heating is discontinued, the autoclave is allowed toreturn to room temperature and excess pressure is discharged. Theautoclave is opened and the reaction mixture is recovered therefromfollowing which the mixture is treated with aqueous caustic to removeany excess unreacted acrylic acid. After drying, the mixture issubjected to gas-liquid chromatographic analysis which will verify thefact that the desired product, commonly named ethyl acrylate, isprepared.

EXAMPLE V A mixture consisting of 160.0 g. of methyl alcohol, 86.0 g. ofmethylacrylic acid and 1.0 g. of palladium acetate and 200.0 g. ofbenzene is placed in the glass liner of a rotating autoclave which isthereafter sealed into the autoclave. After a sufficient amount ofnitrogen is pressed in so that an initial operating pressure of 30atmospheres is reached, the autoclave and contents thereof are thenheated to a temperature of 180C. and maintained thereat for a reactiontime which is of 16 hours duration. At the end of 16 hours, heating isdiscontinued, the autoclave is allowed to return to room temperature andthe excess pressure is discharged. After recovering the reactionmixture, it is treated in a manner similar to that hereinbefore setforth whereby the desired product comprising methyl acrylate isseparated and recovered.

I claim as my invention:

l. A process for the preparation of an ester which comprises reacting acarboxylic acid with an alcohol in the presence of a palladium salt orcomplex at a temperature in the range of from about to about 250 C. anda pressure in the range of from about atmospheric to about 100atmospheres, and recovering the resultant ester.

2. The process as set forth in claim lin which said palladium salt orcomplex is palladium acetate.

3. The process as set forth in claim 1 in which said palladium salt orcomplex is palladium chloride.

4. The process as set forth in claim 1 in which said palladium salt orcomplex is palladium acetylacetonate.

5. The process as set forth in claim 1 in which said carboxylic acid isbenzoic acid, said alcohol is benzyl alcohol and said ester is benzylbenzoate.

6. The process as set forth in claim 1 in which said carboxylic acid isacetic acid, said alcohol is benzyl alcohol and said ester is benzylacetate.

7. The process as set forth in claim 1 in which said carboxylic acid isbutyric acid, said alcohol is benzyl alcohol and said ester is benzylbutyrate.

8. The process as set forth in claim 1 in which said carboxylic acid isacrylic acid, said alcohol is ethyl alcohol and said ester is ethylacrylate.

9. The process as set forth in claim 1 in which said carboxylic acid ismethacrylic acid, said alcohol is methyl alcohol and said ester ismethyl methacrylate.

1. A process for the preparation of an ester which comprises reacting acarboxylic acid with an alcohol in the presence of a palladium salt orcomplex at a temperature in the range of from about 100* to about 250*C. and a pressure in the range of from about atmospheric to about 100atmospheres, and recovering the resultant ester.
 2. The process as setforth in claim 1 in which said palladium salt or complex is palladiumacetate.
 3. The process as set forth in claim 1 in which said palladiumsalt or complex is palladium chloride.
 4. The process as set forth inclaim 1 in which said palladium salt or complex is palladiumacetylacetonate.
 5. The process as set forth in claim 1 in which saidcarboxylic acid is benzoic acid, said alcohol is benzyl alcohol and saidester is benzyl benzoate.
 6. The process as set forth in claim 1 inwhich said carboxylic acid is acetic acid, said alcohol is benzylalcohol and said ester is benzyl acetate.
 7. The process as set forth inclaim 1 in which said carboxylic acid is butyric acid, said alcohol isbenzyl alcohol and said ester is benzyl butyrate.
 8. The process as setforth in claim 1 in which said carboxylic acid is acrylic acid, saidalcohol is ethyl alcohol and said ester is ethyl acrylate.